1. Field of the Invention
The present invention relates to an active matrix organic electroluminescence display device and a method of forming the same, and more particularly to an improvement in a pixel structure of the active matrix organic electroluminescence display device and a method of forming the pixel structure.
2. Description of the Related Art
The active matrix organic electroluminescence display device has an array of pixels, each of which includes a circuitry region and an electroluminescence region which exhibits a luminescence upon application of an electric filed. The circuitry region may often include a thin film transistor having a polysilicon layer.
One of the conventional active matrix organic electroluminescence display device is disclosed in Japanese laid-open patent publication No. 2000-172198. FIG. 1A is a fragmentary plan view illustrative of a single pixel structure of the conventional active matrix organic electroluminescence display device. FIG. 1B is a fragmentary cross sectional elevation view illustrative of a single pixel structure of the conventional active matrix organic electroluminescence display device.
The conventional active matrix organic electroluminescence display device exhibits a luminescence upon application of an electric field to a luminescence region 5. The luminescence is represented by arrow marks. The luminescence may be scattered in a substrate 9, a gate oxide film 13, an inter-layer insulator 15 and on interfaces between them. The scattered light is a stray light which may be incident into a polysilicon layer 12 of a thin film transistor. Further, the luminescence light may be reflected by the substrate 9 so that the reflected light may be a stray light which is incident into the polysilicon layer 12 of the thin film transistor.
The incidence of the stray lights into the polysilicon layer 12 causes the increase in leakage of current of the thin film transistor and the transistor shows a malfunction, whereby a display defect or a display contrast reduction may be caused. This problem becomes more serious as the display gradation becomes large. If the circuitry includes a capacitor and the stray light is incident into a capacitive dielectric layer of the capacitor, then the capacitor becomes unable to hold charges.
It, is therefore, desirable to provide an optical shielding structure which shields the circuitry such as the thin film transistor or the capacitor from the stray light from the luminescence.
The conventional structure shown in FIG. 1B has a planarized insulating layer 25 which may absorb a stray light. The luminescence is, however, omnidirectional. Thus, a part of the luminescence is a light transmitted in a horizontal direction. Such horizontally transmitted light may easily be incident into the polysilicon layer 12.
Other conventional techniques for shielding the thin film transistor from the stray light are disclosed in Japanese laid-open patent publications Nos. 9-80476, 11-84363 and 2000-164875. FIG. 2 is a fragmentary cross sectional elevation view of a pixel structure of the conventional active matrix organic electroluminescence display device, which is disclosed in Japanese laid-open patent publication No. 2000-164875. An optical shield film 26a is provided under the thin film transistor. This conventional optical shielding structure allows an incident of a stray light in a horizontal direction into the polysilicon layer 12 of the thin film transistor.
FIG. 3 is a fragmentary cross sectional elevation view of a pixel structure of the conventional active matrix organic electroluminescence display device, which is disclosed in Japanese laid-open patent publication No. 9-80476. Top and bottom optical shielding layers are provided over and under the thin film transistor. This conventional optical shielding structure allows an incident of a stray light in a horizontal direction into the polysilicon layer 12 of the thin film transistor.
The above conventional optical shielding structures are unable to shield the circuitry such as the thin film transistor from the stray light particularly transmitted in the horizontal direction.
In the above circumstances, the development of a novel active matrix organic electroluminescence display device free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel active matrix organic electroluminescence displayed device free from the above problems.
It is a further object of the present invention to provide a novel pixel structure of an active matrix organic electroluminescence display device free from the above problems.
It is a still further object of the present invention to provide a novel method of forming an active matrix organic electroluminescence display device free from the above problems.
It is yet a further object of the present invention to provide a novel method of forming a structure of an active matrix organic electroluminescence display device free from the above problems.
The present invention provides an active matrix organic electroluminescence display device including: a transparent substrate; a plurality of pixels aligned over the transparent substrate, wherein each of the pixels further includes: a luminescent region which exhibits a luminescence upon application of an electric field; a circuitry region including at least a circuitry; and an optical shielding structure provided between the luminescent region and the circuitry region for shielding the circuitry region from the luminescence from the luminescent region.